Rotary driving device used for rotary actuator

ABSTRACT

A rotary driving device includes a pair of stator magnetic poles having opposing end faces separated by gaps; a rotor of magnetic material rotatably supported inside the stator magnetic pole pair, having two pole surfaces between two planes parallel with the axis of rotation; and an excitation coil of the stator magnetic pole pair. The angular positions of the gaps between the end faces of the stator magnetic pole pair along the circumferential direction are changed along the axial direction, so that output and detent torques are obtained effectively and satisfactorily.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary driving device used for arotary actuator. The rotary driving device according to the presentinvention is used as an actuator for driving, e.g., a rotary valve.

2. Description of the Related Art

A conventional rotary driving device is, for example, constituted bystator magnetic poles, fixed in a housing, and a rotor of a permanentmagnet rotatably supported by a shaft inside the magnetic poles. Thepolarities of the stator magnetic poles are reversed by an excitationcoil, thereby rotating the rotor. The rotor has a cylindrical shape, andthe respective stator magnetic poles are arranged on an identicalcircumference so that distances between inner end faces of the statormagnetic poles and a center of rotation of the rotor become the same.For this reason, lines of magnetic force from the rotor are distributedto be wider than an outer periphery thereof, and a magnetic attractiveforce between the stator magnetic poles and the rotor is weakened.

Therefore, when external rotation or vibration is applied to theexcitation coil in a nonconductive state, the rotor is easily rotatedand cannot maintain a stable rest position. In particular, when a rotarydriving device of this type is compactly formed, i.e., into a shallowouter shape, the outer diameter of the rotor is decreased. Therefore,when the excitation coil is rendered nonconductive, the rest torque ofthe rotor becomes small and a stable rest position cannot be maintained.In addition, when the excitation coil is energized, only a small outputtorque can be obtained from the rotor, for the same reason as describedabove.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its object to provide a compact, improved rotarydriving device which can effectively generate an output torque and adetent torque.

According to the fundamental aspect of the present invention, there isprovided a rotary driving device including: a case defining an outershape of the rotary driving device; a pair of stator magnetic polesfixed inside the case and having end portions opposing through gaps; arotor of magnetic material rotatably supported inside the statormagnetic pole pair and having two pole surfaces between two planesparallel with the axis or rotation; a rotary shaft for rotatablysupporting the rotor; and an excitation coil for generating a magneticforce between the stator magnetic pole pair and the rotor; the positionsof the gaps between the end portions of the stator magnetic pole pairalong the circumferential direction being changed along the axialdirection.

According to another aspect of the present invention, there is provideda rotary driving a device including: a case defining an outer shape ofthe rotary driving device; a rotor of magnetic material rotatablysupported in the case and having at least one pole surface between twoplanes parallel with the axis of rotation; a shaft for rotatablysupporting the rotor; a pair of stator magnetic poles arranged outsiderotor, fixed inside the case, and having end portions opposing eachother with a gap, the position where an attractive magnetic force or arepulsive magnetic force between the end portion of the stator magneticpole and the end portion of the rotor is generated being changedaccording to the rotation of the rotor; and an excitation coil forgenerating a magnetic force between the stator magnetic pole pair andthe rotor.

With the above arrangement, when the excitation coil is energized andthe rotor is rotated, the rotor receives an attractive or repulsiveforce from an end portion or inner surface of the nearest statormagnetic pole in accordance with a rotational angle. Thus, the rotor isstable at any rotational angle, and a large rotational torque can beobtained.

Since the two pole surfaces of the rotor abut against the statormagnetic pole and an upper or lower portion of the rotor opposes aninner surface of the stator magnetic pole, a large detent torque can beobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views showing an example of a prior art rotarydriving device;

FIG. 2 is a sectional view showing a rotary driving device according toan embodiment of the present invention;

FIG. 3 is a perspective view showing an important part of the deviceshown in FIG. 2;

FIG. 4 is a perspective view showing an important part of the deviceshown in FIG. 3;

FIGS. 5A and 5B are sectional views taken respectively along the linesC--C and D--D in FIG. 3 at the stage when the rotor is at the limit ofits counterclockwise rotation and is able to rotate in a clockwisedirection;

FIGS. 6A and 6B are sectional views taken respectively along lines C--Cand D--D in FIG. 3 at the stage when the rotor is at the limit of itsclockwise rotation and is able to rotate in a counterclockwisedirection; and

FIGS. 7 and 8 are graphs showing characteristics of the device shown inFIG. 2, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Before entering into the description of the preferred embodiment, anexample of a prior art rotary driving device for a rotary actuator willbe described with reference to FIGS. 1A and 1B. As shown in FIGS. 1A and1B, a rotary driving device is constituted by stator magnetic poles 82,83, 84, and 85 fixed in a housing 81 and a rotor 87 as a permanentmagnet rotatably supported by a shaft 86 inside the magnetic poles. Thepolarities of the stator magnetic poles 82 and 83 or 84 or 85 arereversed by an excitation coil, thereby rotating the rotor 87.

In the device shown in FIGS. 1A and 1B, the rotor 87 has a cylindricalshape, and the respective stator magnetic poles are arranged on anidentical circumference so that distances between inner end faces of thestator magnetic poles 82, 83, 84, and 85 and a rotating center of therotor 87 are the same. For this reason, lines of magnetic force from therotor 87 are distributed to be wider than the outer periphery of therotor, as shown in FIG. 1B, and the magnetic attractive force betweenthe stator magnetic poles 82, 83, 84, and 85 and the rotor 87 isweakened. When external rotation or vibration is applied to theexcitation coil in a nonconductive state, the rotor is easily rotatedand cannot maintain a stable rest position.

A rotary driving device according to an embodiment of the presentinvention is shown in FIGS. 2, 3, and 4. The rotary driving device shownin FIGS. 2, 3, and 4 is used as a torque motor for switching valves.

Reference numeral 11 denotes a cylindrical case which comprises anonmagnetic member and stores components of the rotary driving device tobe described later in detail. The case 11 is coupled to a housing 71 ofa valve portion 7, and a selector valve is housed in the housing 71.

In the valve portion 7, an output shaft 72 which rotates together with arotor 6 as the rotor is supported by a bearing 18 fixed to the housing71. Reference numeral 19 denotes a plate which comprises a nonmagneticmember and fixes the bearing 18 to the housing 71; and 17, a thrustwasher of the output shaft 72 fixed thereto. The output shaft 72 alsoserves as a valve needle 731, i.e., as a component of the valve portion,and a valve port 732 provided in the axial direction and a valve port733 communicating with the valve port 732 and open to the outerperiphery of the valve needle 731 are provided in the valve needle 731.The valve needle 731 is inserted in a hole 741 of the housing 71. Thehousing 71 is provided with input and output ports 742 and 743 for afluid, thus forming a rotor valve which switches the fluid by rotationof the output shaft 72. When the valve needle 731 is located at aposition shown in FIG. 2, the input port 742, the valve ports 732 and733, and the output port 743 communicate with each other, and open thevalve. However, when the valve needle 731 is rotated from this position,communication between the valve port 733 and the output port 743 isinterrupted, thus closing the valve.

FIG. 3 is perspective view of the main part of the rotary drivingdevice. Reference numeral 21 denotes an excitation coil; 3 and 4, a pairof stator magnetic poles fixed to an inner portion of the case 11 andhaving substantially an arc shape; and 6, a rotor comprising a permanentmagnet which is magnetized in a radial direction so that one side of amagnetized end face exhibits the N pole and the other side exhibits theS pole. It should be noted that a central portion of the rotor 6 neednot be flat. Inner surfaces of the stator magnetic pole 3 and 4 and anouter peripheral end face of the rotor 6 are arranged to be separated ata constant distance.

A yoke 26 transmits an excitation magnetic flux of the excitation coil21 to the stator magnetic poles 3 and 4.

The stator magnetic pole 3 has a substantially arced shape constitutedby an arc portion 3A with end faces 311, 312, 313, 314, 321, 322, and323, and a contact portion 3B with contact surfaces 331 and 341. The endfaces 311, 313, 321, 323, 331, and 341 are parallel to the axis ofrotation of the rotor 6. The end face 312 between the end faces 311 and313 and the end face 322 between the end faces 321 and 323 are inclinedwith respect to the axis of rotation. Positions of the end faces 311,312, 313, 321, 322, and 323 in the circumferential direction aredeviated along the axial direction. A deviation amount is substantiallyequal to a rotational range θ of the rotor 6. The shape of theintermediate end faces 312 and 322 can be referred to as a helical shapewith respect to the axis of rotation.

On the other hand, the contact end faces 331 and 341 of the statormagnetic pole 3 abut against a portion of flat surfaces 61 and 62 of therotor 6, thereby limiting rotation of the rotor and obtaining a largedetent torque. The rotor 6 abuts against the end faces 331 and 441through nonmagnetic members 331a and 441a of, e.g., a rubber or resin,provided thereto and is stopped.

The stator magnetic pole 4 also has opposing end faces 411, 412, 413,422, and 423 and contact end faces 431 and 441 as in the magnetic pole3, and are arranged symmetrical with the axis of rotation. The lengths(g) of gaps 51, 52, 53, 54, 55, and 56 of the opposing end faces of thestator magnetic poles 3 and 4 are set to be equal to each other. Adistance between the surfaces 61 and 62 of the rotor 6, i.e., a height(h) of the rotor 6, is set to be larger than the gap length (g).

The relative positional relationship between the stator magnetic poles 3and 4 and the rotatonal position of the rotor 6 is illustrated in FIGS.5 and 6. At a counterclockwise rotation limit position of the rotor 6(FIGS. 5A and 5B), the rotor 6 abuts against the contact end faces 441and 331 of the stator magnetic poles 3 and 4 through the nonmagneticmembers 441a and 331a. At a clockwise rotation limit position of therotor 6 (FIGS. 6A and 6B), the rotor 6 abuts against the contact endfaces 341 and 431 of the stator magnetic poles 3 and 4 throughnonmagnetic members 341a and 431a.

First, a case will be described wherein the rotor is at thecounterclockwise rotation limit position.

Referring to FIG. 5A, an edge portion 631 of the rotor 6 opposes aportion near the opposing end face 311 of the arc portion 3A of thestator magnetic pole 3, and an edge portion 642 opposes a portion nearthe opposing end face 421 of the arc portion 4A of the stator magneticpole 4. For this reason, in the conductive state, a rotational torquecan be obtained between the stator magnetic poles 3 and 4.

Referring to FIG. 5B, the two edge portions 631 and 632 at one end ofthe rotor 6 and two edge portions 641 and 642 at the other end thereofoppose inner surfaces of the arc portions 4A and 3A of the statormagnetic poles 3 and 4.

A case will be described wherein the rotor is at the clockwise rotationlimit position.

Referring to FIG. 6A, the two edge portions 631 and 632 at one end ofthe rotor 6 and the two edge portions 641 and 642 at the other endthereof oppose inner surfaces of the arc portions 3A and 4A of thestator magnetic poles 3 and 4.

Referring to FIG. 6B, the edge portion 632 at one end of the rotor 6opposes a portion near the end face 413 of the stator magnetic pole 4,and the edge portion 641 at the other end thereof opposes a portion nearthe end face 323 of the stator magnetic pole 3. For this reason, in theconductive state, a rotational torque can be obtained between the statormagnetic poles 3 and 4 and the rotor 6.

As described above, at the positions of FIGS. 5A and 5B, the detenttorque and the output torque are together generated by upper and lowerportions of the rotor 6.

The operation of the device shown in FIGS. 2 and 3 will be describedwith reference to FIGS. 5 and 6.

A magnetic flux (φ₁) as a part of a rest torque at the positions ofFIGS. 5A and 5B forms, due to a magnetic flux generated from the rotorcomprising the permanent magnet, a closed loop as follows: the edgeportion 632 of the rotor 6→the stator magnetic pole 4→the yoke 26→thestator magnetic pole 3→the edge portion 641 of the rotor 6. As shown inFIG. 5B, in the lower portion of the rotor 6, a magnetic flux (φ₂) ispresent to form a closed loop as follows: the edge portions 631 and 632of the rotor 6→the arc portion 4A of the stator magnetic pole 4→the yoke26→the arc portion 3A of the stator magnetic pole 3→the edge portions642 and 641 of the rotor 6. The rotor 6 can generate a large detenttorque by these magnetic fluxes (φ₁, φ₂). In this case, the detenttorque becomes weak with only the magnetic flux (φ₁) at the upperportion of the rotor shown in FIG. 5A, and a magnetic balance is lostdue to variations in size and the like. Therefore, the rotor may beshifted from the position shown in FIG. 5A to the position shown in FIG.6A. However, the detent torque which can satisfactorily hold the rotor 6can be obtained by the magnetic flux (φ₂) at the lower portion (FIG. 6B)of the rotor 6 due to the shapes of the stator magnetic poles 3 and 4.

The operation for generating a rotational force for rotating the rotor 6from the rest position shown in FIGS. 5A and 5B to the position of FIGS.6A and 6B by energizing the excitation coil 21 will be described.

When the stator magnetic poles 4 and 3 are respectively magnetized tothe S and N poles, a repulsive force F(1) is applied to the rotor 6 nearthe end faces 411, 413, 321, and 323 of the stator magnetic poles, andan attractive force F(2) is applied to the rotor 6 near the end faces421 and 323 of the stator magnetic pole. Thus, the rotor 6 is rotated tothe position of FIGS. 6A and 6B. At the same time, the rotor 6 causesthe output shaft 72 to generate the output torque. The rotating force atthis time obtains an activation torque by the upper portion of the rotor(FIG. 5A). This is because, at the position of FIG. 5A, the end faces421 and 311 of the stator magnetic poles oppose the edge portions 642and 641 of the rotor 6. In view of this, a change in magnetic energy Wwith respect to the rotational angle θ of the rotor 6 is large, and theattraction force F(2) is expressed by the following relation, thusobtaining a large activation torque:

    F(2)=dW/dθ(kg)

Meanwhile, since a change in magnetic energy W with respect to therotational angle θ is small at the lower portion of the rotor (FIG. 5B),the lower portion of the rotor does not contribute much to generation ofthe output torque.

Note that when the gaps between the stator magnetic poles 3 and 4 arehelically arranged with respect to the axis of rotation, the outputtorque can be increased within the overall rotational angle θ of therotor 6.

The detent torque and the activation torque at the position in FIGS. 5Aand 6B are also determined by the stator magnetic poles 3 and 4 and therotor 6 as those at the position in FIGS. 6A and 6B.

At the position of FIGS. 6A and 6B, the magnetic flux from the rotor 6is divided at the lower portion of the rotor (FIG. 6B) into a magneticflux (Φ₃) forming the following closed loop: the edge portion 631 of therotor 6→the stator magnetic pole 3→the yoke 26→the stator magnetic pole4→the edge portion 642 of the rotor 6, and at the upper portion of therotor (FIG. 6B) into a magnetic flux (Φ₄) forming the following closedloop: the edge portions 631 and 632 of the rotor 6→the stator magneticpole 3→the yoke 26→the stator magnetic pole 4→the edge portions 642 and641 of the rotor 6. The detent torque is generated from the rotor 6 bythese magnetic fluxes (φ₃, φ₄). As described above, the detent torquecan be stably generated from the rotor 6 by the magnetic flux (φ₄).

When the rotor 6 is at the rest position of FIGS. 6A and 6B, theexcitation coil 21 is energized in a direction opposite to the abovecase so as to generate the N and S poles from the stator magnetic poles3 and 4. Then, an attractive force F(3) is applied to the rotor 6 nearthe end faces 413 and 323 of the stator magnetic poles, and the rotor 6is pivoted counterclockwise from the position shown in FIGS. 5B and 6Bto the position shown in FIGS. 5A-5B. At the same time, the rotor 6causes the output shaft 72 to generate the output torque.

At the lower portion of the rotor (FIG. 6B), the end faces 413 and 323of the stator magnetic poles oppose the edge portions 632 and 641 of therotor 6, thus obtaining a large activation torque.

As described above, according to the present invention, the rotarydriving device can be provided wherein the gap positions of the opposingend faces of the stator magnetic pole pair are provided to be inclinedin a circumferential direction, whereby the upper and lower portions ofthe rotor effectively and satisfactorily generate the output torque andthe detent torque together.

FIG. 7 shows characteristics of the output torque T(OUTPUT) with respectto the rotational angle θ of the rotor, and FIG. 8 shows characteristicsof the output torque T(DETENT) with respect to the rotational angle θ ofthe rotor. Referring to FIGS. 7 and 8, a chain-line curve CURVE-1represents the conventional device shown in FIGS. 1A and 1B, and asolid-line curve CURVE-2 represents the device according to thisembodiment shown in FIGS. 2 and 3.

We claim:
 1. A rotary driving device comprising:a case defining an outershape of the rotary driving device: a pair of arcuate stator magneticpoles fixed inside said case and having end faces opposing through gaps;a rotor of magnetic material rotatably supported inside said statormagnetic pole pair and having two arcuate pole surfaces disposed closelyadjacent said stator poles and between two rotor planar surfacesparallel with the axis of rotation; a rotary shaft for rotatablysupporting said rotor; and an excitation coil for generating a magneticforce between said stator magnetic pole pair and said rotor polesurfaces, the circumferential positions of said gaps being so changedalong the axial direction that a substantially constant rotationalmagnetic force is maintained between said stator poles and said rotorpole surfaces during rotation of said rotor, the width of said gapsbeing smaller than the distance between the two planar surfaces of saidrotor.
 2. A rotary driving device comprising:a case defining an outershape of the rotary driving device; a pair of arcuate stator magneticpoles fixed inside said case and having end faces opposing through gaps;a rotor of magnetic material rotatably supported inside said statormagnetic pole pair and having two arcuate pole surfaces disposed closelyadjacent said stator poles and between two rotor planar surfacesparallel with the axis of rotation; a rotary shaft for rotatablysupporting said rotor; an excitation coil for generating a magneticforce between said stator magnetic pole pair and said rotor polesurfaces; and stop surfaces on the inner surfaces of said statormagnetic poles against which said rotor abuts to restrict the rotaryangle thereof; the circumferential positions of said gaps being sochanged along the axial direction that a substantially constantrotational magnetic force is maintained between said stator poles andsaid rotor pole surfaces during rotation of said rotor.
 3. A rotarydriving device comprising:a case defining an outer shape of the rotarydriving device; a pair of arcuate stator magnetic poles fixed insidesaid case and having end faces opposing through gaps; a rotor ofmagnetic material rotatably supported inside said stator magnetic polepair and having two arcuate pole surfaces disposed closely adjacent saidstator poles and between two rotor planar surfaces parallel with theaxis of rotation; a rotary shaft for rotatably supporting said rotor;and an excitation coil located at a position on the extension of theaxis of rotation of said rotor for generating a magnetic force betweensaid stator magnetic pole pair and said rotor pole surfaces; thecircumferential positions of said gaps being so changed along the axialdirection that a substantially constant rotational magnetic force ismaintained between said stator poles and said rotor pole surfaces duringrotation of said rotor.
 4. A rotary driving device comprising:a casedefining an outer shape of the rotary driving device; a pair of arcuatestator magnetic poles fixed inside said case and having end facesopposing through gaps; a rotor of magnetic material rotatably supportedinside said stator magnetic pole pair and having two arcuate polesurfaces disposed closely adjacent said stator poles and between tworotor planar surfaces parallel with the axis of rotation; a rotary shaftfor rotatably supporting said rotor; an excitation coil for generating amagnetic force between said stator magnetic pole pair and said rotorpole surfaces; and a valve body driven by said device to rotate aboutthe axis of rotation of said rotor for changing the cross-sectional areaof a path of fluid; the circumferential positions of said gaps being sochanged along the axial direction that a substantially constantrotational magnetic force is maintained between said stator poles andsaid rotor pole surfaces during rotation of said rotor.
 5. A rotarydriving device comprising:a case defining an outer shape of the rotarydriving device; a rotor of magnetic material rotatably supported in saidcase and having at least one arcuate pole surface between two rotorplanar surfaces parallel with the axis of rotation; a shaft forrotatably supporting said rotor; a pair of arcuate stator magnetic polesarranged outside said rotor, fixed inside said case, and having endfaces opposing each other with a gap, said gaps being configured so thatthe position where an attractive magnetic force or repulsive magneticforce is generated between one of said stator magnetic poles and saidpole surface of said rotor is changed according to the angular positionof said rotor; an excitation coil for generating a magnetic forcebetween said stator magnetic pole pair and said rotor; and a rotorcontact face on the inner side of at least one of said pair of statormagnetic poles for restricting the rotation of said rotor within arotational angular range between first and second positions by theabutting of a surface of said rotor against said contact face.
 6. Arotary driving device comprising:a case defining an outer shape of therotary driving device; a pair of arcuate stator magnetic poles fixedinside said case and having end faces opposing through gaps; a rotor ofmagnetic material rotatably supported inside said stator magnetic polepair and having two arcuate pole surfaces disposed closely adjacent saidstator poles and between two rotor planar surfaces parallel with theaxis of rotation; a rotary shaft for rotatably supporting said rotor;and an excitation coil for generating a magnetic force between saidstator magnetic pole pair and said rotor pole surfaces, each of saidgaps comprising a pair of circumferentially displaced straight portionsand an inclined portion provided between said straight portions, and anedge portion of each of said pole surfaces of said rotor being arrangedso as to oppose the portion of the stator magnetic pole positioned atsaid edge portion of each of said pole surfaces with a small gaptherebetween when said rotor starts to rotate, the circumferentialpositions of said gaps being so changed along the axial direction that asubstantially constant rotational magnetic force is maintained betweensaid stator poles and said rotor pole surfaces during rotation of saidrotor.
 7. A device according to claim 2, wherein a nonmagnetic member isfixed to each of said contact surfaces.
 8. A device according to claim5, wherein the rotation of said rotor is such that, when said rotor ispositioned at either said first position or said second position, apredetermined part of said pole surface is opposite to the inside of anend portion of a first magnetic pole of said stator magnetic pole pair,while the remainder part of said surface is adjacent to said end portionof said first magnetic pole of said stator magnetic pole pair.